The invention relates in general to the field of drilling equipment and, more particularly, to the use of dual-acting hydraulic drilling jars. Specifically, the invention relates to the conversion of a bidirectional, dual-acting drilling jar to a single-acting drilling jar.
The jar is normally placed in the pipe string in the region of the lodged object and allows the drilling rig operator at the surface to deliver an impact to the fish through manipulation of the drill pipe string. Jars contain a spline joint which allows relative axial movement between an inner mandrel or housing and an outer housing without allowing relative rotational movement. The mandrel or inner housing contains an impact surface or hammer which contacts a similar impact surface or anvil on the housing when the jar has reached the limit of axial travel. If these impact surfaces are brought together at high velocity, they transmit a very substantial impact to the fish due to the mass of the drill pipe above the jar.
Most drilling jobs require that both an upward and downward jar be available in the drilling string. For example, during the drilling of an oil or gas well, the pipe may become stuck due to hole sloughing or differential pressure sticking such that it would be desirable to jar the pipe upward. The pipe may also become lodged in a keyseat while "tripping" (i.e., removing the pipe from the well bore) in which case it would be desirable to jar downward on the stuck point. Bi-directional hydraulic drilling jars are used for such a purpose and are described in U.S. Pat. No. 4,361,195, issued Nov. 30, 1982, and U.S. Pat. No. 5,086,853, issued Feb. 11, 1992, both to Robert W. Evans, which are hereby incorporated by reference in their entirety.
More particularly, U.S. Pat. No. 4,361,195 describes an annular tripping valve that cooperates with a pair of control arms to provide the "dual action." As shown in FIG. 1, the drilling jar of U.S. Pat. No. 4,361,195 is connected in a drill string at its upper threaded opening 2 and connected to a bottom hole assembly to which a jarring action is to be applied at its lower threaded connection 4 or sub 6. To provide a downward jarring function, tension force is released from the upper drill pipe, thereby placing it under compression. This, in turn, applies a compressive force downward against mandrel 8 and attempts to move the mandrel downward in relation to housing 10. The initial downward movement of mandrel 8 occurs relatively freely, with the movement being a sliding movement relative to housing 10 and to pressure pistons 12 and 14. During this phase of movement, shoulder 16 of sleeve member 18 is brought into engagement with the top surface of pressure piston 12. At this point, further movement of mandrel 8 will cause shoulder 16 to move pressure piston 12 downward inside fluid pressure chamber 22. Thus, the movement causes pressure piston 12 to move away from shoulder 20 on which it is positioned when the apparatus is in the neutral position shown in FIG. 1.
Such movement of pressure piston 12 by shoulder 16 of mandrel 8 causes actuating members or control arms 24 to move the end flange portion 26 until it engages the end flange 28 on tripping valve member 30. Further movement of pressure piston 12 will cause tripping valve member 30 to be moved while maintaining the same relative position to valve opening 32. As tripping valve member 30 moves downward, tripping valve member 34 follows valve member 30 in downward movement under the influence of spring 36 and the elevated pressure in chamber 22 compresses both valve parts tightly together. When the valve member 34 is moved downwardly by the pressure in chamber 22 and spring 36 (i.e., following the movement of valve member 30 by control arm 24), valve member 34 is moved relative to control arm 40 extending from lower pressure piston 14. The end flange 42 of control arm 40 remains in a stationary position, while valve member 34 moves past it, until end flange 44 of valve member 34 engages flange 42. At this point, any further movement of pressure piston 12 toward piston 14 will cause the relative movement of control arms 40 and 24 to begin to separate the valve members 34 and 30 which comprise tripping valve 46.
Up to this point, the relative movement of pressure piston 12, pressure piston 14, and control arms 24 and 40 has been described as if the movement were unobstructed. It should be noted, however, that fluid pressure chamber 22, which is enclosed by pressure pistons 12 and 14, as well as tripping valve 46, is a completely closed chamber except for the very small opening or orifice 48 through piston 12. The downward movement of piston 12 pressurizes the hydraulic fluid in chamber 22. The fluid pressure resists movement of the piston. As the compressive force applied to mandrel 8 is increased by the weight applied by the drill string above the drilling jar, the hydraulic pressure in fluid chamber 22 increases as a result of the load imposed on pressure piston 12. The check valve 50 in pressure piston 14 prevents the flow of fluid outward through piston 14. The closed valve members 34 and 30 of tripping valve 46 also prevent the flow of hydraulic fluid from the chamber at that point. It should be noted that the closed valve members 34 and 30 are urged into tighter closure due to the elevated pressure in chamber 22 acting on an annular area from the valve seal point to the outer surface 52 of sleeve 54. The only point of exit of fluid from chamber 22 during this phase of operation is through the very small bleed passage 48 in piston 12. The size of bleed passage 48 is such that the hydraulic fluid can flow through it at a very slow rate only when subjected to a relatively high pressure.
As the force applied to pressure piston 12 increases, piston 12 tends to move downward in chamber 22, however, it is resisted by the fluid in the chamber and can move only as fluid leaves through orifice 48. The fluid in chamber 22 is therefore maintained under a very high pressure and, as piston 12 moves slowly downwardly to maintain the pressure in chamber 22, fluid flows from chamber 22 through opening 48. When pressure piston 12 has moved downward to the point where end flanges 26 and 42 of control arms 24 and 40 have reached engagement with the end flanges 44 and 28 of valve members 34 and 30 and forced the valve members to separate, the hammer 56 on mandrel 8 has moved only a fraction of the distance downward toward anvil 58. At this point, mandrel 8 is under a very high compressive force applied by the drill string above and will release that force to move hammer 56 at a high speed and with a high impact against anvil 58 whenever the resistance to further movement is released.
Further downward movement of pressure piston 12 relative to piston 14 will cause the end flanges 26 and 42 of control arms 24 and 40 to move valve members 34 and 30 apart to open the tripping valve 46. When the tripping valve 46 is opened, the fluid in hydraulic fluid chamber 22 is permitted to flow out through the opened tripping valve 46, opening 32, and the various passages to the various fluid chambers which are not under elevated pressure. Thus, when tripping valve 46 is opened, the fluid in chamber 22 can flow through passages 60 and 62 into fluid chamber 64 located above the downwardly moving pressure piston 12. Fluid is also free to move from chamber 22 through passage 60 downwardly into fluid chamber 66 above pressure balancing piston 68. This sudden release of fluid from chamber 22 releases virtually all resistance to downward movement of pressure piston 12. At this point, piston 12 moves rapidly downward under the influence of the high potential energy built up by the compression and weight of the drill string. The rapid downward movement of piston 12 allows mandrel 8 to move along with it very rapidly and causes hammer 56 to bring hammer face 70 into engagement with anvil surface 58 with a very high impact force. For the sake of brevity, the description of upward jarring, which is quite similar to downward jarring is described in detail in U.S. Pat. No. 4,361,195, and is incorporated here by reference.
U.S. Pat. No. 5,086,853 describes a hydraulic tripping valve in a drilling jar that cooperates with alternating pairs of flanges to provide both upward and downward jarring. The jar of U.S. Pat. No. 5,086,853 is shown in FIG. 2. As discussed in conjunction with the jar of U.S. Pat. No. 4,361,195, mandrel 72 and, consequently, actuating mechanism 76, move downward relative to housing 74.
Mandrel 72 moves sufficiently downward so that flange 76 is longitudinally moved and contacts actuating surface 78 of valve member 80, at which point, neither of valve members 82, 80 of tripping valve 84 are longitudinally displaced by movement of mandrel 72. Also, coil springs 86, 88 will generally maintain the position of tripping valve 84 at its central location in chamber 90.
As mandrel 72 and flange 76 move further downward, they will carry with them tripping valve 84. At this point, valve members 82, 80 will still have not separated, owing to the force of coil springs 86, 88, combined with the rising internal pressure of chamber 90. It will be appreciated that the downward movement of mandrel 72 carries with it upper piston 92, thereby reducing the volume of chamber 90 and, consequently, increasing the internal pressure. The internal pressure of chamber 90 acts against the outer surfaces of the valve members 82, 80 and urges them together to maintain their closed position. The tripping valve 84 is carried downward to a point where flange 94 on the valve member 82 engages flange 96 of housing 74.
Continual downward movement of mandrel 72 and flange 76 forces valve members 82, 80 into their separated or "open" position. The upper valve member 82 is restrained against further downward movement by the interaction of flange 94 and housing flange 96. However, further downward movement of mandrel 72 forces flange 76 against actuating surface 78 of lower valve member 80, causing it to separate from upper valve member 82. With high pressure chamber 90 opened to passages 98, hydraulic fluid quickly flows out of chamber 90 and reduces the pressure therein. With the pressure in chamber 90 substantially reduced, downward movement of the mandrel relative to housing 74 is no longer resisted by a substantial force. Thus, mandrel 72 now moves rapidly downward into housing 74 causing hammer 100 to sharply strike lower anvil surface 102. In contrast, an upward jarring action begins by mandrel 72 being withdrawn or pulled upward and out of housing 74. The upward jarring motion is similar to the downward jarring motion except flanges 104, 96 and 76 are used as described in detail in the U.S. Pat. No. 5,086,853 patent.
A drill string in a well is typically several thousand feet in length. Gravity acts on the drill string causing a downward force to be placed on the drill string; the downward force of gravity is countered by an upward force exerted by the object that is holding the drill string. The two opposing forces causes the portion of the drill string above the neutral point to be stretched (i.e., have a tensile force applied). In contrast, the bottom hole assembly (i.e., the portion of the drill string below the neutral point which contains the drilling bit) is constantly encountering undrilled formations. The resistance of formations to movement results in an upward force being placed on the drill bit; the force of gravity associated with the weight of the bottom hole assembly exerts a downward force on the drill bit. These two opposing forces cause the bottom hole assembly to be in compression.
If a drilling jar is to be placed in the bottom hole assembly close to the drill bit, the ability to have a single-acting drilling jar becomes desirable. Typically, drilling jars have a maximum pressure that must be met in order for them to "cock" (i.e., prepare to exert an impact). When drilling jars are placed in the bottom hole assembly, the jar experiences the compressive forces associated with that region. The ratio of the compressive forces to the area is equivalent to pressure; if the pressure from compressive forces becomes greater than the pressure requirement for "cocking", the jar will prepare to exert a downward jar. When an unexpected downward jar occurs in the bottom hole assembly, there can be major repercussions. For example, it may be undesirable to jar downward when drilling in a hard formation because of possibly damaging the drill bit.
The present invention is directed towards overcoming some of the disadvantages of she prior art by providing a drilling jar that jars in the upward direction and only "bumps" in the downward direction.